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Description: Ultrasonic scanning experiments were conducted for detecting defects in wood pallet parts using rolling transducers. The characterization of defects is important for sorting and grading pallet parts, as well as for manufacturing quality and durable pallets. This paper reports the scanning results for stringers and deckboards – the two main components of pallet for red oak and yellow-poplar species. Sound and unsound knots, bark pockets, decay, splits, holes, and wane were characterized using several ultrasonic parameters. Each ultrasonic waveform collected was characterized using eight ultrasonic variables – three involving time of flight, two involving ultrasound pulse energy, one using ultrasound pulse duration, and peak frequency. The amplitude of ultrasound signals was significantly reduced by defects. The degree of dispersion of the power spectrum mostly depends on the severity and type of defects. The energy loss parameters are more sensitive to defects compared to time of flight measurements. Unsound knots, bark pockets, decay, holes, and splits are easily detectable and distinguishable using power spectrum, energy loss, and peak frequency parameters. Two-dimensional images were constructed from multi-line scanning data for each sample. The constructed images are able to show the exact location and area of the defects. Scanning properties of this prototype system suggest that an on-line system to inspect, sort, and grade wooden pallet parts is possible using rolling transducer ultrasonic inspection.

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